Catalytic hydrogenation of aromatic epoxy resins, for example, diglycidyl ether of bisphenol A and diglycidyl ether of bisphenol F, produces cycloaliphatic diepoxides. Cycloaliphatic diepoxides are useful as weatherable coatings components in marine coatings, in protective coatings (for example, oil and gas segment, storage tanks, bridges, industrial architecture) and in electronic materials applications.
Catalytic hydrogenation of aromatic epoxides to form cycloaliphatic epoxides can be carried out in one step. However, the challenge for a process of catalytic hydrogenation of aromatic epoxides is the ability to fully (for example, up to about 98% or more) hydrogenate the aromatic rings and at the same time retain the epoxy groups, since epoxy groups can be destroyed by hydrogenation. Heretofore, supported rhodium catalysts have been preferably used in known processes for the catalytic hydrogenation of aromatic epoxides based on the supported rhodium catalysts' high activity (for example, wherein the reaction activity of the catalyst allows for reaction completion within several hours at temperatures of less than about 60° C.) and high selectivity (for example, wherein the reaction selectivity of the catalyst allows for retention of epoxy groups at greater than about 85% at aromatic hydrogenation of greater than about 98%) to cycloaliphatic epoxides.
For example, a cycloaliphatic epoxy resin product can be produced by the hydrogenation of an epoxy resin in the presence of a catalyst and in the presence of a solvent as illustrated by the chemical reaction scheme, Scheme (I), which follows which shows a cycloaliphatic epoxy resin such as a cycloaliphatic diglycidyl ether produced via direct catalytic hydrogenation of a commercial bisphenol A or bisphenol F diglycidyl ether at room temperature (about 25° C.).

A problem with the use of known rhodium catalysts in the above catalytic hydrogenation process is that the catalysts have been found to undergo a rapid deactivation under the process conditions, typically reducing activity twice with every subsequent cycle.
U.S. Pat. No. 3,966,636 discloses a process for the regeneration of a deactivated rhodium (Rh) and ruthenium (Ru) catalyst by sequentially contacting the deactivated catalyst first with a hydrogen-containing gas then with an oxygen-containing gas and finally with a hydrogen-containing gas. In the above process, Rh or Ru supported on an alpha alumina carrier is used as the catalyst; and methylene dichloride (CH2Cl2) is used as a reactivation solvent. The above patent advocates the use of a multistep and lengthy procedure employing a hydrogen-containing gas at 150° C. to 600° C. and an oxygen-containing gas at 75° C. to 450° C. The complexity and high temperatures employed in the above known procedure makes this approach impractical for reactivating a deactivated catalyst.
US 2011/0196171 A1 discloses a process for producing a hydrogenated aromatic polycarboxylic acid and teaches the use of a primary catalyst of Rh supported on carbon (C) in combination with a secondary catalyst of palladium (Pd) or platinum (Pt) supported on C for the hydrogenation of aromatic carboxylic acids. The method of regenerating the catalyst is carried out by a washing step with water; and the oxidation of the catalyst is carried out by an air oxidation step at room temperature (about 25° C.). The above patent application does not disclose hydrogenating an aromatic epoxide. Also, the examples in the above patent application use water as a solvent; and water is not an acceptable solvent for the aromatic epoxide hydrogenation to aliphatic epoxide due to hydrolysis of epoxy groups in the presence of water.
Other processes for the catalytic hydrogenation of bisphenol A diglycidyl ether are disclosed, for example, in U.S. Pat. Nos. 3,336,241; 4,847,394; 5,530,147; 5,614,646; and 6,130,344; and U.S. Patent Application Publication No. 20040176549. The above prior art, however, does not disclose a suitable process for regenerating a catalyst after the catalyst has been used for hydrogenating bisphenol A diglycidyl ether and related aromatic epoxies. Typically, the catalysts used in the above known processes contain expensive precious metals such as rhodium and/or ruthenium; and a one-time use of such precious metal catalysts is uneconomical.